1. Field of the Invention
The present invention relates to an intake manifold for use with an automobile gasoline engine or an automobile diesel engine.
2. Description of the Related Art
In common, an intake manifold for use with a gasoline engine for an automotive vehicle is provided, as shown in a schematic view of FIG. 5, in which a plurality of branch tubes 53 are connected at one end to a flange 51 joined to an intake port of the engine and at the other end to a surge tank 52 joined to a throttle chamber. As the assembly including the branch tubes 53 and the surge tank 52 is generally formed by metal casting, the freedom for designing the passage of the branch tubes 53 is lowered due to various limitations of the casting such as the separation of molds. Also, the distribution of molten metal requires a considerable thickness of casting, hence increasing the overall weight of a casting. For the purpose of eliminating such a problem, an intake manifold is disclosed in Japanese Patent Laid-open Publication (Hei)4-350353 in which the branch tubes 53 are fabricated by bending and joining by brazing in a furnace a set of aluminum alloy pipes at both ends to the flange 51 and the surge tank 52 of aluminum casting.
The joining the branch tubes 53 to the flange 51 and the surge tank 52 by brazing in a furnace provides high air-tightness at the joints thus allowing the mass production. However, the joining by brazing in a furnace where they are heated up under a high-temperature atmosphere with a brazing material being melted may cause thermal deformation due to a difference in the thermal capacity between the two materials to be joined. For example, as shown in an enlarged cross sectional view of FIG. 6, the branch tubes 53 are dislocated from their correct position to the brazing region 54 of the surface tank 52 and may decline their function. Also, as the assembly is placed under such a high-temperature atmosphere in the furnace, the branch tubes 53 of aluminum alloy and the surge tank 52 of aluminum casting are possibly annealed hence decreasing the physical strength. Particularly in case that the joint portion is formed with threaded holes for tightening stays and brackets by means of screws, the physical strength of the joint portion will significantly be declined.